1. Field of the Invention
The present invention relates to signal tracking. More particularly, the invention relates to a method and apparatus that utilize an estimated and a measured signal characteristic to efficiently detect emitter movement.
2. Description of the Related Art
The ability to track signals is becoming increasingly important as the use of wireless communications devices becomes commonplace throughout the world. For example, the U.S. Federal Communications Commission Enhanced 911 (E911) rules will eventually require cellular telephone carriers to identify the geolocations, i.e. the physical source locations, of subscribers who place emergency calls to 911 or other services. Additionally, wireless communication device users often desire to acquire accurate geolocations for navigation purposes, such as to generate a route between a current location and a destination. Further, military and law enforcement agencies often desire to locate sources of emitted signals for tracking and targeting purposes.
To assist in signal tracking and geolocation determination, it is often desirable to detect if signal emitters are moving or stationary. Methods and systems have been developed to detect emitter movement utilizing repeated, complex, and time consuming calculations. For example, some of these methods include continuously calculating geolocations of emitted signals and comparing currently calculated geolocations to previously calculated geolocations to determine if geolocations have changed. Unfortunately, continuously calculating geolocations requires multiple measurements and calculations over a substantial period of time, thereby increasing the cost and time required to detect emitter movement.
Other developed methods of detecting emitter movement include utilizing several collection systems and/or several signal measurements to detect emitter movement utilizing a plurality of discrete signal measurements. Although such methods may be more efficient than continuously calculating geolocations, they require complex and costly systems, such as a network of at least four collector elements, or include often inaccurate assumptions regarding emitter velocity, thereby reducing their effectiveness. Thus, the ability to accurately detect emitter movement is often limited due to the lack of functionality of developed methods and systems.